<html>
<title> BAI KIEM TRA GHP</title>
<FORM METHOD = POST ACTION="#">	
<center><h1><b><font color="orgrance">BAI KIEM TRA GHP </font></h1></u>
      <br>
   <b><i><font color= "orgrance">NHAP VAO SO NGUYEN N:</font></i></b>
   <INPUT  TYPE= "char" NAME ="a" SIZE="20">
      <br><br>
   <input type="submit" name="text" value="TONG TU 1-N">
   <BR>
   <input type="reset" name="text" value= "IN RA BAN CUU CHUONG N"> 
   <font color="orgrance" size="30"> 
   <BR>
   </html>
	<?php
$a = $b = $c = "";
                    if(isset($_POST['btnok'])){
                        if($_POST['a'] == NULL){
                            echo "nhap so  thu nhat<br/>";
                        }else{
                            $a = $_POST['a']; 
                        }
                        if($_POST['b'] == NULL){
                            echo "nhap so thu hai ";
                        }else{
                            $b = $_POST['b']; 
                        }
                        if($a && $b){
                            $c = $a + $b;
                        }
                    }

?>